I'm seeing a lot of wrong solutions to "fixing" MySQL to work after upgrading to Snow Leopard. Like reinstalling it completely or having MacPorts install its version.
MySQL's Preference Pane grays out its start button after an upgrade. The only reason why this is is because somehow the upgrade procedure to Mac OS X 10.6 removed /usr/local/mysql which is what the Preference Pane looks for.
All that's needed is putting this file back. And in fact the file is a symlink to your "real" mysql installation which they haven't touched.
Here's the fix:
Change the directory to /usr/local by doing: `cd /usr/local/`
`ls` should list one or more mysql folders.
`sudo ln -s mysql-<the version you'd like to use> mysql`
And there you go, you've re-created the link to MySQL. The link for which the preference pane was looking. Restarting System Preferences picks up the link and you can start MySQL again.
What should be noted is that MySQL does not provide a 64 bit version of their preference pane yet. But you can download a 64 bit compiled one from here: http://www.swoon.net/site/software.html
Another good idea might be to install a 64 bit version of MySQL if you hadn't done so, as your OS is now fully 64 bit...
I hope Google will pick up this little post and rank it highly before all the FUD that's been generated online :)